| Message ID | 1334125848.5300.2330.camel@edumazet-glaptop |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
On Wed, 2012-04-11 at 08:30 +0200, Eric Dumazet wrote: > Marc Merlin reported many order-1 allocations failures in TX path on its > wireless setup, that dont make any sense with MTU=1500 network, and non > SG capable hardware. > > After investigation, it turns out TCP uses sk_stream_alloc_skb() and > used as a convention skb_tailroom(skb) to know how many bytes of data > payload could be put in this skb (for non SG capable devices) > ... > > Reported-by: Marc MERLIN <marc@merlins.org> > Tested-by: Marc MERLIN <marc@merlins.org> > Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> David, I forgot to say this should be backported to 3.2 & 3.3 commit 87fb4b7b533073 (net: more accurate skb truesize) did the placement of skb_shared_info at the end of skb head, so sk_stream_alloc_skb() had to reserve more room so that tailroom stayed at MSS -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Eric Dumazet <eric.dumazet@gmail.com> Date: Wed, 11 Apr 2012 08:30:48 +0200 > Marc Merlin reported many order-1 allocations failures in TX path on its > wireless setup, that dont make any sense with MTU=1500 network, and non > SG capable hardware. > > After investigation, it turns out TCP uses sk_stream_alloc_skb() and > used as a convention skb_tailroom(skb) to know how many bytes of data > payload could be put in this skb (for non SG capable devices) > > Note : these skb used kmalloc-4096 (MTU=1500 + MAX_HEADER + > sizeof(struct skb_shared_info) being above 2048) > > Later, mac80211 layer need to add some bytes at the tail of skb > (IEEE80211_ENCRYPT_TAILROOM = 18 bytes) and since no more tailroom is > available has to call pskb_expand_head() and request order-1 > allocations. > > This patch changes sk_stream_alloc_skb() so that only > sk->sk_prot->max_header bytes of headroom are reserved, and use a new > skb field, avail_size to hold the data payload limit. > > This way, order-0 allocations done by TCP stack can leave more than 2 KB > of tailroom and no more allocation is performed in mac80211 layer (or > any layer needing some tailroom) > > avail_size is unioned with mark/dropcount, since mark will be set later > in IP stack for output packets. Therefore, skb size is unchanged. > > Reported-by: Marc MERLIN <marc@merlins.org> > Tested-by: Marc MERLIN <marc@merlins.org> > Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> Applied and queued up for -stable, thanks Eric. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Eric Dumazet <eric.dumazet@gmail.com> Date: Wed, 11 Apr 2012 09:38:02 +0200 > David, I forgot to say this should be backported to 3.2 & 3.3 Yep. > commit 87fb4b7b533073 (net: more accurate skb truesize) did the > placement of skb_shared_info at the end of skb head, so > sk_stream_alloc_skb() had to reserve more room so that tailroom stayed > at MSS Will keep that in mind, thanks. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 3337027..70a3f8d 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -481,6 +481,7 @@ struct sk_buff { union { __u32 mark; __u32 dropcount; + __u32 avail_size; }; sk_buff_data_t transport_header; @@ -1366,6 +1367,18 @@ static inline int skb_tailroom(const struct sk_buff *skb) } /** + * skb_availroom - bytes at buffer end + * @skb: buffer to check + * + * Return the number of bytes of free space at the tail of an sk_buff + * allocated by sk_stream_alloc() + */ +static inline int skb_availroom(const struct sk_buff *skb) +{ + return skb_is_nonlinear(skb) ? 0 : skb->avail_size - skb->len; +} + +/** * skb_reserve - adjust headroom * @skb: buffer to alter * @len: bytes to move diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 5d54ed3..87f497f 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -701,11 +701,12 @@ struct sk_buff *sk_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp) skb = alloc_skb_fclone(size + sk->sk_prot->max_header, gfp); if (skb) { if (sk_wmem_schedule(sk, skb->truesize)) { + skb_reserve(skb, sk->sk_prot->max_header); /* * Make sure that we have exactly size bytes * available to the caller, no more, no less. */ - skb_reserve(skb, skb_tailroom(skb) - size); + skb->avail_size = size; return skb; } __kfree_skb(skb); @@ -995,10 +996,9 @@ new_segment: copy = seglen; /* Where to copy to? */ - if (skb_tailroom(skb) > 0) { + if (skb_availroom(skb) > 0) { /* We have some space in skb head. Superb! */ - if (copy > skb_tailroom(skb)) - copy = skb_tailroom(skb); + copy = min_t(int, copy, skb_availroom(skb)); err = skb_add_data_nocache(sk, skb, from, copy); if (err) goto do_fault; diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 364784a..376b2cf 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -2060,7 +2060,7 @@ static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to, /* Punt if not enough space exists in the first SKB for * the data in the second */ - if (skb->len > skb_tailroom(to)) + if (skb->len > skb_availroom(to)) break; if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))